The present invention relates to a dashpot provided on a carburetor of an internal combustion engine for preventing a throttle valve thereof from closing too suddenly.
An internal combustion engine for a motor vehicle is equipped with a dashpot in order to slowly close a throttle valve. If the throttle valve is suddenly closed after the driver releases an accelerator pedal, the air-fuel mixture gets excessively rich, resulting in stalling of the engine or backfiring.
The dashpot generally comprises a body, the inner space of which is divided into an atmosphere chamber and a pressure chamber by a diaphragm, an actuating rod operatively connected to a throttle valve and attached to the diaphragm, and a spring for urging the diaphragm in a direction so as to expand the pressure chamber. As the diaphragm is displaced by the throttle valve through the rod against the urging of the spring, the air in the pressure chamber flows into the atmosphere chamber through an orifice formed in the diaphragm. Since the flow rate of the air passing through the orifice is very small, the movement of the diaphragm is dampened, thereby slowly closing the throttle valve.
However, such a dashpot has only a simple operational mode so that it cannot cope with various decelerating conditions of the vehicle.
Publications of Japanese Utility Model Laid Open 55-35356 and 55-167552 disclose a throttle-return check device comprising two dashpots, having different operational strokes, disposed in tandem. One of the dashpots is selected dependent on the vacuum in the intake manifold downstream of the throttle valve. Accordingly, the device provides different dampening effects for different decelerating conditions.
However, since such a device comprises two dashpots, the number of the components thereof increases and hence the control system becomes complicated, increasing its manufacturing cost.